1. Field of the Invention
The present invention relates to a medium stacker for an output device that employs paper, such as a printer and a copier, and more particularly to a medium stacker for an output device in which a detachable expanding module is provided to increase the ascending range of a stacker tray that stacks papers ejected from a main body of the output device and to expand the capacity of the stacker tray.
2. Discussion of the Related Art
A related art medium stacker for a medium unit of an output device that employs paper, such as a copier and a printer, includes a stacker tray that stacks papers ejected to the outside of the output device. The stacker tray ascends with respect to a main body of the output device to stack the papers thereon. The related art medium stacker will be described with reference to FIG. 1.
As shown in FIG. 1, the related art medium stacker includes a stacker tray 107, upper and lower pulleys 103 and 104, a driving motor 105, and a power transmission system 106. The stacker tray 107 is provided to move up and down along a main body frame 101 of an output device by rotation of a closed curve belt 102. The upper and lower pulleys 103 and 104 rotatably fix and support the closed curve belt 102. The driving motor 105 is provided inside the main body frame 101 and provides a rotational force for driving the closed curve belt 102. The power transmission system 106 transmits the rotational force of the driving motor 105 to the lower pulley 104.
The position of the stacker tray 107 is determined by the capacity of stacking the papers ejected from a medium unit 110 of the main body of the output device. If many stacked papers are provided, the stacker tray 107 move downwardly.
The operation of the aforementioned related art medium stacker will be described below.
Papers 10 finished in the main body of the output device are ejected outwardly through the medium unit 110 and then stacked on the stacker tray 107. If a great number of papers are stacked on the stacker tray 107, the stacker tray 107 descends by a predetermined distance so as not to allow the completely stacked papers to interrupt ejection of new papers. That is, if the power is applied to the driving motor 105 in accordance with the capacity of the papers, the rotational force is transmitted to the lower pulley 104 through the power transmission system 106. As a result, the closed curved belt 102 is driven in a direction of arrow xe2x80x9cAxe2x80x9d and the stacker tray 107 connected with the closed curve belt 102 descends in a direction of arrow xe2x80x9cb.xe2x80x9d
Therefore, the ejected papers 10 can be stacked on the stacker tray 107 without any interrupt of the completely stacked papers.
However, the aforementioned related art medium stacker has several problems.
Since the stacker tray 107 ascends by means of the closed curve belt 102, the ascending operation is limited to the range between the upper and lower pulleys 103 and 104. This limits the number of papers that can be stacked on the stacker tray 107.
To increase the capacity of the papers on the stacker tray 17, it is necessary to increase the length of the closed curve belt 102 by increasing the distance between the upper and lower pulleys 103 and 104. In this case, a new power transmission structure is required.
Moreover, if the stacker tray 107 is in contact with an external object while it descends, the rotational force of the motor 105 acts on the stacker tray 107 through the closed curve belt 102. This may cause overload and damage of the medium stacker or the object which is in contact with the stacker tray 10.
The present invention is directed to a medium stacker that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a medium stacker in which a stacker tray ascends by means of a non-closed curve belt having a predetermined length, elastically fixed to a frame so as not to directly transmit a driving force of a motor to the stacker tray if an external force prevents the stacker tray from descending.
Another object of the present invention is to provide a medium stacker in which a detachable expanding module is provided to increase the ascending range of a stacker tray without change of a power transmission structure, thereby increasing the capacity of papers on the stacker tray.
Other object of the present invention is to provide a medium stacker having a structure that effectively processes load externally applied to a stacker tray so as to prevent damage of the medium stacker and an external object from occurring.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the scheme particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a medium stacker includes a basic module frame fixed to a medium unit of a main body of an output device, a stacker tray fixed to the basic module frame to enable the ascending operation, on which ejected papers are stacked, a first guide means provided in the basic module frame, guiding the ascending operation of the stacker tray, a lifting belt ascending the stacker tray along the first guide means, a belt driving pulley fixed to the lifting belt, and a power transmission system rotating the belt driving pulley, wherein the lifting belt includes a first part moving along the belt driving pulley, fixed to the stacker tray and a second part of an elastic member which is not moving along the belt driving pulley.
The lifting belt has a non-closed curve type in such a way that the first part has one end fixed to the stacker tray and the second has one end fixed to the basic module frame.
The first part of the lifting belt is provided with teeth engaged with the belt driving pulley, and the second part is formed of a spring member.
The medium stacker further includes an expanding module frame detachably fixed to the lower part of the basic module frame, the expanding module frame being provided with a second guide means connected with the first guide means.
The medium stacker further includes a sensing means that senses the position of the stacker tray. The sensing means includes a first sensing plate of a conductive material arranged in the basic module frame in parallel with the first guide means, having slits arranged at predetermined intervals, and a plate spring of a conductive material fixed to the stacker tray, sensing the position of the stacker tray in contact with the slits of the first sensing plate in accordance with the ascending operation of the stacker tray.
The sensing means further includes a second sensing plate of a conductive material arranged in the basic module frame in parallel with the second guide means, having slits arranged at predetermined intervals, and the plate spring senses the position of the stacker tray in contact with the slits of the second sensing plate in accordance with the ascending operation of the stacker tray.
The medium stacker further includes adhesive rollers fixed to adjoin the belt driving pulley, adhering the first part of the lifting belt to the circumference of the belt driving pulley.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.